Making Adobe Bricks

Abobe brick making is a simple technology: all one really requires is dirt, water, and a hole in the ground to mix the two--- with the "bricks" being formed by hand. The process can be greatly expanded, all the way up to using front loaders or brick-making machines. The method used depends upon how many bricks are required, how much labor (people) one is willing to pay, and how quickly one wants bricks. One may also purchase bricks already made.

Making an adobe brick requires a great deal of dirt. A five-gallon bucket with a full load of dirt will make almost three "Traditional New Mexico" size bricks four inches thick, ten inches wide, and fourteen inches long (4x10x14). A brick this size will weigh about thirty pounds. One also needs adobe mortar between each brick, figured at about one-half inch thick, ten inches wide, and fourteen inches long (1/2x10x14).

How many bricks do you need? A great many! Long, long rows of them. Even a small shack will require a considerable amount.

Suppose you want a wall ten inches thick, eight feet tall, and fifteen feet long. That is 10 inches thick, 96 inches tall, and 180 inches long. Using "Traditional New Mexico" size bricks, divide the height of the desired wall in inches (96) by the thickness of the brick (4) and the result is 24. (Since the mud mortar between the bricks will be around 1/2 inches thick, one will actually need fewer bricks to achieve this eight feet in height, but bricks break so it is good to estimate without the mortar thickness.) This means your wall must be 24 bricks tall.

Now take the length of the wall in inches (180) and divide it by the length of the brick (14) and you will get 12.86 which you may round up to 13. This means you need thirteen bricks laid end-to-end to get a line fifteen feel long.

Now multiply the number of bricks to get eight feet tall (24) by the number of bricks to get fifteen feet long (13). You will see that it takes aproximately 312 bricks to make that one wall. To make a one-room shack that is fifteen feet square and eight feet tall, you will need 1,248 bricks. A room fifteen feet square would probably make a nice bedroom.

Doors and windows will cut down on the number of bricks required. However, it is a good idea to calculate the number of bricks based on wall size without windows and doors, as many of the bricks will not be usable.

One may make adobe brick forms out of 2x4x10 wood studs. The inside space should be the size of the brick you desire. For the "Traditional New Mexico" size, the inside space should be 10 inches by 14 inches, with the 2x4 resting on its 2-inch side. You might wish to also include a handle on both ends to help lift the form free of the mud once the mud has set for a few hours.

The left image shows a small form, filled with mud. The mud has been shoveled in and then smoothed by hand. This small form was used to test various mud mixtures--- for production of bricks, one will use larger forms. The large forms require smoothing via use of a 2x4 piece of wood that may be put on the end of a pole, which will rest along the side rails of the form so that excess mud may be pushed off, as in the image to the right.

The size of the adobe brick will depend on one's desired wall thickness, and how much weight per brick one and one's workers are able to lift comfortably. An abobe brick 4x12x18 inches will weigh about fifty pounds, which will be difficult for many people to work for several hours a day. To put that into perspective, a plastic five-gallon jug of water weighs 41.7 pounds (at 8.34 pounds to a gallon of water), which means an adobe brick 4x12x18 will be about eight pounds heavier than a typical water cooler bottle of water; a brick 4x10x14 will be about ten pounds lighter than a five-gallon water bottle.

This image shows adobe bricks drying while resting on their edges. Once the mud has been setting in the forms for a few hours, the forms are lifted up and excess dirt is knocked off the forms. The forms need not be washed before being used again: a puddy knife may be used to scrape them free of excess clumps of dirt.

Once the forms are removed, the bricks should be left laying flat for about three days, and only then placed upon their edges. In the image to the left one can see the corners of the two damp bricks at the bottom turning white: this shows they were ready to be placed on their edges. The four bricks still laying flat show no white edges yet, so they remain laying flat.

The two bricks in the middle that are on their edges are almost dry: they needed another week to be fully dry. This is a good time to use a puddy knife and scrape off excess mud from the brick, and shape it properly if there are any bulges. One may also use one's hands, with work gloves on, to brush away the excess clumps from the bricks.

After one has made some test bricks, one will wish to drop them to see how brittle they are. In the image above I droped two bricks on their corners, from a height of about four feet--- they both shattered. This means that the bricks were made of far too much sand and not enough clay. Bricks should be able to survive the drop with little or no damage.

A good brick will have the right mixture of clay and sand, so that it will be strong and resist moisture (from the clay content), but not crack while drying. If cracks show, this means there is too much clay in the dirt, and sand should be added. Too little clay and the brick will be too brittle.

This is the result after doing a kick test on the other two bricks. I used tennis shoes and kicked the bricks in their middles without using much force in the kick. These bricks were made from sand found in the Imperial Valley, California, about thirty miles West of Yuma, Arizona: this material is totally unsuitable for adobe brick construction (obviously).

What to look for when looking for dirt with which to build.

Dirt suitable for adobe brick should have a high enough clay content to help the brick resist moisture and provide strength to the brick. The problem is that dirt with too much clay in it will crack upon drying. If dirt has too much clay, one must add sand to it or dried grass; sand is the better additive. Dirt with too little clay will mean that the dried brick will be too brittle to use.

Fortunately, the margin for error is rather wide. Dirt from the side of a hill usually works; avoid dry wash beds or valley floors where sandy dirt has collected due to gravity and erosion. The tops of hills will usually be good for dirt. Dirt from a hill that has lasted a hundred thousand years or so without being washed away will probably be good enough to make adobe bricks out of--- that is, most hills that have not been man-made.

The best way to know if a pile of dirt is good enough to make adobe bricks out of is to make test bricks--- three or four will do. If the brick is dropped from four or five feet onto one of its corners and there is little damage, the dirt will very likely be usable for building.

One may also mix a bucket of dirt with a little water and see how well the dirt adhears it itself--- if it can be molded and rolled into balls, but pulls apart with only a little effort, then it is worth trying test bricks with the dirt. If it pulls apart too easily, or does not form into balls easily, then the sand content is probably too high and the dirt will probably not be worth using for test bricks.

It might take three or four tries to find the right dirt mixture, or you might stumble upon a working source of dirt the first time you look. Remember that you will need a large pile of dirt for a modest sized building.